bump gtk-vnc dependency to 0.3.6

[Jonh Wendell <jwendell gnome org>]

Hi, folks.

Can we bump external gtk-vnc dependency to 0.3.6? I need some features
of it for Vinagre 2.23.2 (trunk).

Just for your information, I'm also a developer of gtk-vnc, and, as soon as I find out some Vinagre bugs, they need to be fixed in gtk-vnc. That's why I need the very latest version of it.

Thanks,
-- 
Jonh Wendell
www.bani.com.br